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| United States Patent | 5,294,255 |
| Smetana , et al. | March 15, 1994 |
A pumpable backfill grout which hardens into a controlled low strength material and an additive for making up such a backfill grout. The grout consists essentially of portland cement, a smooth surfaced vesicular expanded perlite, fly ash, fine aggregate, water, an air entraining agent, a quick dispersing thixiotropic suspending agent and a bentonite thickening agent.
| Inventors: | Smetana; David A. (Cleveland, OH); Lenczewski; Richard J. (Cleveland, OH); Wilson; Alfonzo L. (Cleveland, OH) |
| Assignee: | Specrete-IP Incorporated (Cleveland, OH) |
| Appl. No.: | 949435 |
| Filed: | September 23, 1992 |
| Current U.S. Class: | 106/698; 106/675; 106/705; 106/706; 106/708; 106/709; 106/719; 106/DIG.2; 252/378P; 405/266 |
| Intern'l Class: | C04B 014/08; C04B 014/18 |
| Field of Search: | 106/675,677,698,705,706,708,709,718,719,724,738,820,823,DIG. 1,DIG. 2 252/378 P 405/266,267 |
| 4419135 | Dec., 1983 | Hoge | 106/678. |
| 5114617 | May., 1992 | Smetana et al. | 106/DIG. |
______________________________________
Material Parts by Weight
______________________________________
vesicular 500-1200
expanded perlite
air entraining agent
100-200
diatomaceous earth 25-75
quick dispersing thixiotropic
25-75
suspending agent
bentonite thickening
10-35
agent
dispersant 10-35.
______________________________________
______________________________________
Material Parts by Weight
______________________________________
vesicular 500-1200
expanded perlite
air entraining agent
100-200
diatomaceous earth 25-75
quick dispersing hydroxy ethyl
25-75
cellulose thixiotropic
suspending agent
bentonite thickening
10-35
agent
calcium lignosulfonate
10-35.
______________________________________
______________________________________
portland cement 60-300
fly ash 250-350
fine aggregate 2500-3000
water 400-700
vesicular 3-15
expanded perlite
air entraining agent
.6-1.2
diatomaceous earth .15-.45
quick dispensing thixiotropic
.15-.45
suspending agent
bentonite thickening
agent .06-.2
dispersant .06-.2.
______________________________________
______________________________________
portland cement 60-300
fly ash 250-350
fine aggregate 2500-3000
water 400-700
vesicular 3-15
expanded perlite
air entraining agent .6-1.2
diatomaceous earth .15-.45
quick dispensing hydroxyethyl
.15-.45
cellulose thixiotropic
suspending agent
bentonite thickening .06-.2
agent
caclium lignosulfonate
dispersant .06-.2.
______________________________________
______________________________________
Material Parts by Weight
______________________________________
smooth surfaced vesicular
500-1200
expanded perlite
air entraining agent
100-200
diatomaceous earth 25-75
quick dispersing thixiotropic
25-75
suspending agent
bentonite thickening
10-35
agent
dispersant 10-35.
______________________________________
______________________________________
Material Parts by Weight
______________________________________
smooth surfaced vesicular
500-1200
expanded perlite
air entraining agent
100-200
diatomaceous earth 25-75
quick dispersing hydroxy ethyl
25-75
cellulose thixiotropic
suspending agent
bentonite thickening
10-35
agent
calcium lignosulfonate
10-35.
______________________________________
______________________________________
portland cement 60-300
fly ash 250-350
fine aggregate 2500-3000
water 400-700
smooth surfaced vesicular
3-15
expanded perlite
air entraining agent
.6-1.2
diatomaceous earth .15-.45
quick dispensing thixiotropic
.15-.45
suspending agent
bentonite thickening
.06-.2
agent
dispersant .06-.2.
______________________________________
______________________________________
portland cement 60-300
fly ash 250-350
fine aggregate 2500-3000
water 400-700
smooth surfaced vesicular
3-15
expanded perlite
air entraining agent .6-1.2
diatomaceous earth .15-.45
quick dispensing hydroxyethyl
.15-.45
cellulose thixiotropic
suspending agent
bentonite thickening .06-.2
agent
caclium lignosulfonate
dispersant .06-.2.
______________________________________
Description
BACKGROUND OF THE INVENTION
This invention relates to low strength concrete compositions to be used as
back fill grouts. These compositions are capable of solidifying into
inexpensive, low strength materials for back filling excavations where it
is desirable to avoid subsidence of the back filled materials subsequent
to the back filling operation. They are pumpable with sufficient viscosity
to remain free of settling out or separation of components during pumping,
and are of low enough viscosity to take advantage of the void-filling
capability of the grout.
As is known in the art, an admixture is a material other than hydraulic
cement, water, fiber reinforcement or aggregates which is used as an
ingredient of concrete or mortar and is added to the batch immediately
before or during its mixing or use. Admixtures are used to modify the
properties of concrete or grout in such a way as to make it more suitable
for a particular purpose or for economy. Using an admixture should allow
the employment of less expensive construction methods or designs or
achieve new results and thereby offset the costs of the admixture. U.S.
Pat. No. 4,961,790 discloses additional information regarding admixtures
generally, and is hereby incorporated by reference.
The present invention concerns the use of an admixture for increasing the
viscosity of a cementitious grout or blend containing a high proportion of
aggregate and a very low proportion of cement which, without the
admixture, would be of very limited use due to the settling of the
aggregate from the mixture.
One material commonly used to fill cavities is referred to as CLSM,
Controlled Low Strength Material. This material can be discharged from the
chute of a ready mix truck directly into the cavity to be filled,
whereupon the material will set into a low strength concrete useful for
filling cavities resulting from excavation operations. When such a cavity
is inaccessible by truck or where it is necessary for the material to flow
or be pumped over some distance to its final destination, CLSM material
presents difficulties and generally can not be used due to separation and
settling out of the aggregate contained in such mixtures.
SUMMARY OF THE INVENTION
The present invention relates to a novel pumpable cementitious mixture of
the CLSM type which is hardenable into a low-strength concrete
particularly useful as an inexpensive back fill grout, which is especially
useful in applications where subsequent subsidence of the back filled
volume must be prevented, and in which the avoidance of settlement or
separation of components is important. The particular advantage of the
mixture is that it is pumpable and thereby useful in certain applications
in which sufficient viscosity to prevent separation and settling out of
the aggregate is very important, but in which an inexpensive mixture is
also required. The novel aspects of this mixture include a relatively
smooth-surfaced, vesicular, expanded perlite, which is relatively hard and
not friable, but which has low density so that it floats in water, and is
of a fine grain size, intermediate that of normally used aggregates and
that of dry cements and an air entraining agent, diatomaceous earth, a
thickening agent, and a dispersant.
The present invention further relates to a novel blend of components for an
admixture to be added to a CLSM to attain the desired characteristics of
pumpability and suspension stability. The addition of said admixture to a
CLSM enables the CLSM blend of materials to be pumped into place. The
admixture of the present invention provides lateral flow with excellent
mobility a stable, homogenous mixture, volume stability with less than 1%
bleeding, and an increase of approximately 16% in yield.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The cementitious composition of the present invention contains, based on
the wet grout or cementitious mixture, from about 0.01 to 10 percent by
weight of a relatively smooth-surfaced, vesicular, expanded perlite of
from about 100 to 30 mesh in size, with a bulk density of from about 7 to
20 pounds per cubic foot. It is relatively hard and not friable. It does
not disintegrate when used as an aggregate and mixed with cement and other
aggregates.
This material is described in U.S. patent application Ser. No. 07/571,549,
filed Aug. 24, 1990, now U.S. Pat. No. 5,114,617. It is available from
Specrete-IP Incorporated of 10703 Quebec Avenue, Cleveland, Ohio 44106.
A key characteristic of this expanded perlite is that it does not segregate
when blended and shipped with other dry materials, and it resists
degradation when blended with other materials. This result is in contrast
to the performance of the prior art expanded perlite, which tends to
segregate and degrade when mixed with other materials.
Another key characteristic of this expanded perlite is that, by weight,
over 60% of it floats in water. By volume, most of it floats in water and
only a small portion sinks in water.
In addition, as will be hereinafter described, the cementitious
composition, of this invention contains an air entraining agent,
diatomaceous earth, a thickening agent, and a dispersant or surface active
agent.
Table I lists several formulations for presently known and employed prior
art controlled low-strength materials (CLSM). These CLSM formulations are
believed to be typical or representative of the formulations used and
strengths produced when used in applications calling for a low-strength
concrete material, e.g., with design strengths in compression ranging from
50 to 1000 psi. All of the following design strengths are for strengths in
compression.
TABLE I
______________________________________
Typical CLSM Mix Proportions
______________________________________
Design Strength, psi
50 100 500 1000
Cement, lb. 60 100 190 280
Fly Ash, lb. 290 300 300 300
Fine Aggregate, lb.
2770 2700 2680 2650
Water, lb. 475 465 460 440
______________________________________
The mixes of Table I above can be poured or placed into a cavity. The
placement, however, must be continuous or subsidence will take place. It
will become immobile and it will not be possible to move the material
further into the cavity. If you want to turn a typical CLSM mix into a
flowable motar, you have to add more water. By a "flowable motar", it is
meant that the material will not become immobile as it is being poured or
placed even though, after it has been poured or otherwise placed, it may
subside. By "subside", it is meant that the solids separate out from the
liquid leaving a liquid layer and a layer of mixed solids.
A flowable 100 p.s.i. design strength CLSM mortar mix is as follows:
TABLE II
______________________________________
Design Strength, psi
100
Cement, lb 100
Fly Ash Aggregate, lb
300
Fine Aggregate, lb
2600
Water, lb 584
______________________________________
While the above mix is flowable, it is still not pumpable in the
conventional sense and it still subsides.
By the use of a small amount of the admixture of my invention, however, a
100 p.s.i. design strength pumpable grout can be made as follows:
TABLE III
______________________________________
PUMPABLE BACK FILL GROUT
______________________________________
Design Strength, psi
100
Cement, lb 100
Fly Ash, (C), lb 300
Fine Aggregate, lb
2600
Expanded perlite 8
additive (Table VI)
Water 485
______________________________________
The Table III pumpable CLSM formulation provides a design strength of 100
psi, as does the flowable mortar formulation shown in Table II. The
formulations are similar in amount of cement, fly ash and fine aggregate
employed. The pumpable back fill formulation grout has less water.
However, as shown in Table IV below, significant differences exist in the
physical properties of the material thus formed. The volume is
considerably larger in the pumpable back fill grout of the present
invention, and consistently therewith the density of this material is much
lower. The laboratory observations, shown also in Table IV, clearly
demonstrate the physical and functional differences between the two
formulations.
TABLE IV
______________________________________
CONTROLLED LOW STRENGTH MATERIAL
______________________________________
Prior Present
Art CLSM Invention CLSM
(Table II)
(Table III)
______________________________________
Design Stength, psi
100 100
Yield, ft.sup.3
27.5 >32.0
W/C + FA Rati
1.46 1.21
Wet Density, lb/ft.sup.3
138 105
______________________________________
Laboratory Observations
Pumping Placeable, but
Homogenous
Characteristics
problematic Mixture -
Readily pumped
Mobility/ None 35-40 sec./
Lateral Flow 1/2" flow cone
Subsidence/ Substantial/ <1% in one hour
Settlement Rapid
Volume Stability
Settlement/ Maintains >99%
Bleeding Measured Volume
Fluidifying Increased
Admixture Subsidence
______________________________________
Of particular interest and concern in the present invention is the
difference in pumpability. The CLSM back fill grout of the present
invention greatly increases the viscosity of the mixture, allowing the
material to be easily pumped over considerable distances with no danger of
settling out of suspended aggregate during the pumping process, thus
greatly improving the pumping characteristics over the prior art. The
mobility/lateral flow test of Table IV, refers to the time taken for the
mortar admixture to flow through a cone having a one-half inch orifice.
The prior art flowable mortar could not be measured due to the fact that
the water rapidly separated out from the solids and the solids blocked the
orifice. As noted, subsidence or settlement and volume stability refer to
the propensity of the solids of the mortar to settle out and expell the
water. As clearly shown in Table IV, the pumpable back fill grout of the
invention is superior in these respects as well.
The fact that the expanded perlite of the invention has a smooth surface
which is nearly sealed, and over 60% of it by weight floats in water,
accounts primarily for the differences in volume and density of these two
100 p.s.i. design strength formulations as shown in Table IV.
The other factor is the entrainment of air brought about by the addition of
an air entrainment agent. This helps in placing the grout and prevents the
loss of volume from loss of water caused by subsidence.
Table V below gives typical ranges of weights of the ingredients in an
expanded perlite additive formulation. These ranges are useful for
producing pumpable back fill grouts having various characteristics, but
all within the scope of the invention.
TABLE V
______________________________________
Expanded Perlite Additive Formulation
for Back Fill Grout
Material Parts by Weight, lb
______________________________________
Expanded perlite 500-1200
Air Entraining Agent
100-200
Diatomaceous earth
25-75
Quick dispersing 25-75
thixotropic suspending
agent
Bentonite thickening
10-35
agent
Dispersant 10-35
______________________________________
The preferred air entraining agent is Vinsol Resin NVX 20% neutralized
solution. This is an extract from southern pine stump wood. It is a dark
high melting thermoplastic resin which has been reacted with alkalis to
neutralize it and produce water soaps. It is manufactured by the Hercules
Powder Company of Wilmington, Del. Other suitable air entraining agents
are DARAVAIR and DAREX sold by Grace Concrete Products of Chicago, Ill.
These air entraining agents comply with ASTM Designation 260.
The preferred diatomaceous earth is Dicalite. This is produced by Grefco,
Inc. of Torrence, Calif.
The preferred quick dispersing thixotropic suspending agent is Cellosize QP
4400H. This is a hydroxy ethyl cellulose manufactured by Union Carbide
Chemicals and Plastics of Bound Brook Company, N.J. Other quick dispersing
thixotropic suspending agents are CARBOPOL 801 sold by BF Goodrich of
Cleveland, Ohio, and STYMER S sold by Monsanto Chemical Company of Saint
Louis, Mo. CARBOPOL 801 is a polyacrylic acid powder. STYMER S is a sodium
salt of a styrene-maleic anhydride copolymer.
The term "dispersant" is intended to cover surface active agents which,
when added to water, promote uniform and maximum separation of extremely
fine solid particles. For the most part, they are polymeric electrolytes.
The preferred bentonite thickening agent is Quick Gel Bentonite
manufactured by Barold Drilling Fluids of Houston, Tex. It is both a
viscosifier and thickening agent. This bentonite is preferred because it
is quick wetting. Other bentonites may be used if they have suitable
wetting characteristics. When properly dispersed and wetted, the bentonite
also has thixiotropic effects. It is not, however, quick dispersing.
The preferred dispersant or surface active agent is Weschem CA-1 calcium
lignosulfonate. This is manufactured by Wesco Technologies Ltd. of San
Clemente, Calif. It is a refined calcium lignosulfonate powder.
Small amounts of sodium hexametaphosphate may be used as a dispersant.
Superplasticizer powders such as BOREM 100 HP sold by Boremco Specialty
Chemical of Fall River, Mass., may be used as a disperant. The
superplasticizers tend to be expensive.
The preferred formulation for the backfill grout additive of my invention
is given in Table VI below.
TABLE VI
______________________________________
Back Fill Grout Additive Formulation
Material Weight, lb
______________________________________
Expanded perlite 850
Vinsol Resin (20%) 155
Diatomite 50
Cellosize QP4400H 50
Quick Gel Bentonite 25
Wesco CA 1 (Calcium Lignosulfonate)
25
______________________________________
A typical backfill grout wet mix formulation, ready to be pumped, is as
follows:
______________________________________
Ingredient Parts by Weight
______________________________________
portland cement 60-300
fly ash 250-350
fine aggregate 2500-3000
water 400-700
smooth surfaced vesicular
3-15
expanded perlite
air entraining agent
.6-1.2
diatomaceous earth .15-.45
quick dispersing .15-.45
thixotropic suspending agent
bentonite thickening agent
.06-.2
dispersant .06-.2
______________________________________
While some of the benefits of the present invention may be obtained with
open-surfaced vesicular expanded perlite, such as PERMALITE, sold by
Chemrock Corporation of Nashville, Tenn., it is not the preferred
material. The particles are larger than the smooth surface expanded
perlite, they are not as hard and they are more friable. In an additive
formulation, such as Table V, when shipped, they may separate.
While the invention has been shown and described with respect to particular
embodiments thereof, the examples are for the purpose of illustration
rather than limitation, and other variations and modifications of the
specific embodiments herein described will be apparent to those skilled in
the art all within the intended spirit and scope of the invention.
Accordingly, the invention is not to be limited in scope and effect to the
specific embodiment herein described, nor in any other way that is
inconsistent with the extent to which the progress in the art has been
advanced by the invention.
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